A given base station of a cellular network has limited coverage. In order to provide service to users that move between geographic locations, handover procedures have been implemented that allow for a communication session on a mobile device to transition from a serving base station to a target base station as the mobile device moves away from the serving base station and toward the target base station. This allows the user to continue a communication session (e.g., a voice call) while moving between geographic locations. To initiate a handover procedure, a mobile device takes radio signal strength measurements from the serving base station and compares these measurements to a handover triggering threshold previously received from the serving base station. If a measurement is below the threshold, a handover procedure is triggered so that an ongoing communication session can be transitioned to a target base station.
However, using a single handover triggering threshold is suboptimal in view of the “heterogeneous” nature of current cellular networks that support both legacy technologies and new technologies. For example, consider a legacy mobile device using a legacy technology (e.g., a narrowband audio codec) for a voice call served by a particular base station, and a new mobile device using a newer technology (e.g., a super wideband audio codec) for a voice call served by the same base station. Both the legacy device and new device will initiate respective handover procedures at the same radio signal level, which is determined by the single handover triggering threshold provided by the serving base station to each device. Because the new device uses newer technology that may extend the distance from the serving base station that the new device can stay on the communication session, the single handover triggering threshold can trigger a handover procedure for the new device earlier than necessary. Since there is an inherent risk of dropping a communication session during a handover procedure, this introduces an unneeded risk of a dropped communication session for the new device. If the handover triggering threshold provided by the serving base station is lowered to accommodate the extended coverage of the new device, the lowered threshold does not work for the legacy device due to the more limited coverage provided by the legacy technology it uses. For example, as the legacy device moves away from the serving base station, the lowered threshold may not even be crossed before the communication session of the legacy device is dropped.